Our long term goal is to understand the pathophysiological role of voltage-dependent Ca2+ channels in epilepsy and other neurological disorders. Among the four subunits comprising the mammalian Ca2+ channel (alpha1, alpha2delta, beta, gamma), the gamma subunit is the least well understood. Originally copurified with the 1,4-dihydropyridine receptor (L-type Ca2+ channel) from skeletal muscle, early studies centered on the ability of the 32 kDa transmembrane gamma subunit to modulate the electrophysiological properties of the channel. Other possible functions went largely unexplored. A focus on the regulation of Ca2+ currents as the function of the gamma subunit continued after identification of a novel neuronal isoform (CACNG2, gamma2) that is mutated in the stargazer (stg) mouse, a valuable animal model of inherited epilepsy and ataxia. Our laboratory has now identified 6 more Ca2+ channel gamma subunit genes: CACNG3-CACNG8. It was recently determined that the gamma2 subunit interacts with PDZ domain proteins (PSD-95 and others) and is essential for the proper membrane localization and synaptic targeting of AMPA-type glutamate receptors in cerebellar neurons. Based on these data, and preliminary analysis of CACNG3-CACNG8, we hypothesize that Ca2+ channel gamma subunits are primarily involved in the formation and targeting of multifunctional synaptic protein complexes in neurons, and that regulation of Ca2+ currents may be only a subsidiary function. The specific aims of this project are to: 1) determine the spatial and developmental expression of the wild-type Ca2+ channel gamma subunit genes (CACNG 1-8) and proteins (gamma1-8) in brain; 2) characterize binding of the gamma subunits to (a) PDZ domain proteins, (b) each other, and (c) novel proteins; and 3) determine whether loss of the gamma2 subunit in the Cacng2-null stargazer (stg) mouse results in altered expression of Cacng1-8 in brain, or altered steady-state association of gamma3, gamma4, and gamma8 with PDZ domain proteins. These systematic studies will provide invaluable insight into the basic function of the Ca2+ channel gamma subunits, the structure and localization of protein complexes at neuronal synapses, and the molecular mechanisms of inherited epilepsy and ataxia.